[en] In the mare, oocytes in vitro maturation protocols are still in development. To our knowledge, immature oocyte aspect under light microscopy has not been studied and compared with mature oocyte aspect. The aim of the study is to give a general description of immature oocytes and the relationships between the different aspects.
Follicles from ovaries obtained at slaughterhouse are punctured after measurement of their diameter. Different characters, such as oocyte diameter, cumulus aspect, granulosity and polarity of ooplasm are observed under light microscopy.
No correlation between oestral activity, follicle maturity, cumulus cells aspect, polarity and granulosity of ooplasm was observed. Thickness of zona pellucida differs between oocytes with polar or non polar ooplasm, but no other parameter studied showed an influence on oocyte diameter. No correlation was observed between follicle diameter and oocyte diameter.
Results show that no character observed under light microscopy is related to oocyte follicular origin or to any other character. Further studies have to be done to compare these oocytes with mature oocytes and to find the ultra-structural origin of characters observed under light microscopy.